The present invention relates in general to electronic circuits and in particular to logic circuits.
The growth and maturity of the electronics industry has led to a variety of products that have changed the way people live and work. Electronic circuits are currently the dominant technology for creating products that move and shape information. In the world of electronics, information is typically represented by zeros and ones. Electronic representations of zeros and ones are referred to as digital signals. Electronic circuits process digital signals using logic circuits to perform a wide variety of functions.
However, as the electronics industry continues to grow, there is an ever increasing demand on the amount of information that must be processed by electronic circuits. Accordingly, the speed at which these electronic circuits operate has continually increased. An electronic circuit's processing speed is determined by the frequency of the signals. For example, some electronic circuits carry out a processing operation on each rising edge of a system clock. These circuits are referred to as “synchronous” circuits. Therefore, the processing speed of the circuit will be determined by the frequency of the clock.
As the operating frequency of electronic circuits continues to increase, the timing relationships between signals can severely limit the performance of the system. For example, if a clock signal triggers the execution of a function requiring two digital input signals, the function will produce an erroneous result if the clock signal triggers the function before one or both of the digital inputs are available for processing. The time period during which a signal is typically stable is determined by the transitions of the signals. For example, if a circuit output signal transitions from a low voltage to a high voltage in response to a first set of inputs, and then from the high voltage to a low voltage in response to a subsequent set of inputs, then the output of the circuit will be stable for a period of time determined by the transitions from low to high and high to low voltages. However, typical logic circuits will have different transition characteristics in response to different sets of inputs, which can deleteriously affect timing requirements. Accordingly, there is a need for logic circuits with improved transition characteristics.